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Planting forests of quick-growing trees in the world’s most arid deserts and sustaining them with desalinated water from nearby oceans would cool the regions significantly and draw down billions of tons of carbon dioxide, according to climate simulations being published in the journal Climatic Change. The concept, proposed by cell biologist Leonard Ornstein of the Mount Sinai School of Medicine in New York, includes transporting desalinated water to parched deserts with aqueducts and pumps to support growth of such heat-resistant trees as eucalyptus. By watering the plants with drip irrigation, in which water is sent directly to the trees’ roots via plastic tubing, engineers could reduce water loss, says Ornstein, who calculated the climatic effects with NASA modelers. According to the models, planting heat-resistant trees in the Sahara Desert or the Australian outback could draw down about 8 billion tons of carbon annually. In the case of the Sahara, temperatures in the forests could drop by as much as 8°C. The costs of building and running reverse-osmosis plants for desalination and transporting the water would be about $2 trillion per year. “Any solution to climate change has to be a multitrillion-dollar project,” Ornstein says. “The issue is what the payback is.”